Insertion of Internal Alkynes and Ethene into Permethylated Singly Tucked-in Titanocene

Abstract

The singly tucked-in permethyltitanocene 1 reacts with an excess of internal alkynes to give the 1:1 adducts 3a−c,f−i, arising from insertion of the alkyne triple bond into the titanium−methylene bond. Only the simplest species, 2-butyne, inserted two molecules to give the known compound 2; however, at a 1:1 stoichiometric ratio the 1:1 adduct 3j was also smoothly formed. 1,4-Disubstituted conjugated diynes with CMe3 or SiMe3 substituents reacted in the same way by only one triple bond to give 3d,e, respectively. The dimethylsilylene-bridged dialkynes Me2Si(CCR)2 (R = SiMe3, CMe3) afforded compounds 3k,l with both triple bonds reacting. After insertion of the first triple bond, the second one underwent a rearrangement which resulted in substituent shift and formation of a silacyclobutene ring linked to the titanium atom. Alkynes bearing the bulky substituents CMe3 and SiMe3 were unreactive. Among a number of olefins and 1,3-butadiene, only ethene reacted to give cleanly the 1:1 adduct 3m. The structures of the paramagnetic [TiIII(η5-C5Me5){η5:η1-C5Me4(CH2CR1CR2)}] products 3a−g,k,l were determined by single-crystal X-ray diffraction analysis. These compounds and compounds 3h−j,m, whose crystal structures could not be determined, were chlorinated with PbCl2 to give the diamagnetic products [TiIVCl(η5-C5Me5){η5:η1-C5Me4(CH2CR1CR2)}] (4a−j) and the corresponding chlorotitanocene derivatives 4k−m. The solution structures of 4a−m were determined by 1H and 13C NMR spectroscopy, and crystal structures for 4b,e,g,l,m were found by single crystal X-ray diffraction analysis. DFT calculations threw light on the transition-state molecule for the formation of 3j and revealed a steric hindrance to be responsible for preventing the insertion of a second molecule of hex-3-yne, the closest homologue of but-2-yne, to react with 3i, forming a homologue of 2.

[1-Dimethylsilyl-2-phenyl-3-(η5-tetramethylcyclopentadienyl)prop-1-en-1-yl-κC1](η5-pentamethylcyclopentadienyl)titanium(III)

“…Instead, the known type of structure was obtained, which was formed by an insertion of the substituted alkyne into the titanium-methylene bond of the titanocene derivative, while the SiMe 2 H substituent stayed intact. Notably, only the described regioisomer was isolated as the preferentially crystallizing product of the insertion, which is in line with previous findings (Pinkas et al, 2008). Observed geometrical parameters (for numbering scheme, see Fig.…”

Thermolysis of titanocene methyl compounds bearing t-butyl- and benzyltetramethylcyclopentadienyl ligands

“…The benzyl carbon atom C(110) lies almost exactly in the leastsquares plane of the tethered cyclopentadienyl ring, and the angle C(15)ÀC(110)ÀC(111) of 110.8(3)°is close to the theoretical value for sp 3 carbon atom. The valence angles at the ipso-carbon atom C(110)ÀC(111)ÀC(116) and C(110)ÀC(111)ÀC(112) as well as the C(111)ÀC(112)ÀTi(1) angle are virtually equal (118.5-118.7(3)°) and the Ti(1)ÀC(112) bond length of 2.263(3) Å falls into the range of TiÀC@ distances in permethyltitanocenes with one cyclopentadienyl ring tethered to titanium with a 3-membered C@CÀC chain [16]. The presence of some strain in the phenyl ring is indicated by a large Ti(1)ÀC(112)ÀC(113) angle of 127.3(2)°and a small C(111)ÀC(112)ÀC(113) angle of 113.8(3)°.…”

“…1 H NMR (C 6 D 6 , 300 Hz): À3.29, À1.06 (2 Â d, 2 Â 2 J HH = 9.9 Hz, 2 Â 1H, TiCH 2 CMe 2 ); 0.89 (m, 1H, TiCH 2 ); 1.07 (s, 3H, C 5 Me 3 ); 1. 16 A suspension of [TiCl 2 (g 5 -C 5 Me 4 CH 2 Ph) 2 ] (1.080 g, 2.0 mmol) in hexane (50 ml) was poured onto solid LiMe made by evaporation of 5 ml of 1.6 M solution in vacuum, finally at 80°C. The mixture was shaken at 60°C until all red titanocene dichloride was consumed (ca.…”

Synthesis and crystal structure of the singly tucked-in derivative of bis(phenyltetramethylcyclopentadienyl)titanium

“…Compound 9 was paramagnetic, giving a broad signal at g = 1.954, resembling the EPR spectra of [Ti(III)Me(g 5 -C 5 Me 5 ) 2 ] and similar alkyltitanocene compounds (g = 1.952-1.959) or that of 1 (g = 1.954) [7,15]. In contrast to electronic absorption spectra of alkyltitanocene compounds, which display two absorptions in the visible region (460-490 and 595-655 [2c,7], compound 9 showed only single absorption band at 580 nm, similar to that of 1 (k 550 nm [2c, 16]). The EI-MS spectra of 9 showed the molecular ion m/z 441 as a base peak which fragmentated with a loss of hydrogen or elimination of the cyclopentadienyl ligand and varying amount of hydrogen (low abundant m/z 242-237).…”